Language-activated cerebral blood oxygenation and hemodynamic changes of the left prefrontal cortex in poststroke...

In normal subjects, regional cerebral blood flow (rCBF) is greatly increased by neuronal activity, whereas the cerebral metabolic rate for O2 is increased only slightly. However, it is not clear what kinds of cerebral blood oxygenation and hemodynamic changes can be induced by language activities in language-relevant areas of poststroke aphasics. In the present study, we investigated the difference in the changes of cerebral blood oxygenation and hemodynamics in the left prefrontal cortex induced by language activities between normal subjects, poststroke nonaphasic patients, and nonfluent aphasic patients using near-infrared spectroscopy (NIRS).

Twenty-nine participants performed speech tasks, such as confrontational naming, to evaluate changes among poststroke nonfluent (Broca's) aphasia patients (10 cases; mean+/-SEM, 56.9+/-2.2 years), age-matched normal subjects (13 cases; 50.7+/-2.2 years) and poststroke nonaphasic patients (6 cases; 52.5+/-3.9 years). The optodes of NIRS were placed over the left prefrontal cortex. We analyzed the NIRS parameter (oxyhemoglobin [oxy-Hb], deoxyhemoglobin [deoxy-Hb], and total hemoglobin [total-Hb]) changes by qualitative pattern analysis of the parameter changes and quantitative analysis of the parameter values among the groups.

The most common NIRS parameter change was an increase in oxy-Hb and total-Hb, with a slight decrease or no change in deoxy-Hb in the normal subjects (5 of 13 cases, 38.5%) and the nonaphasic cerebrovascular disease (CVD) patients (3 of 6 cases, 50.0%). In contrast, the most common pattern in the aphasic patients was an increase of deoxy-Hb, with an increase of oxy-Hb and total-Hb (5 of 10 cases, 50%). However, this pattern was observed in only 3 of 13 cases (23.1%) in the normal subjects and 1 of 6 cases (16.7%) in the nonaphasic CVD patients. The mean (+/-SEM) changes of deoxy-Hb of the aphasic patients, the normal subjects, and the nonaphasic CVD patients were 0.78+/-0.29, 0.06+/-0.16, and -0.18 +/- 0.22, respectively. The statistical analysis demonstrated a significant effect for deoxy-Hb (P<0.05), with the aphasic patients differing significantly from the normal subjects and the nonaphasic CVD patients, while the 2 nonaphasic groups did not differ from each other.

The present results demonstrate a multiplicity of language-activated cerebral blood oxygenation and hemodynamic changes in the left prefrontal cortex in the nonaphasic and aphasic groups. The increase of deoxy-Hb with increases of oxy-Hb and total-Hb in the aphasics during language tasks suggests that the left prefrontal cortex of the aphasics utilizes more oxygen than the nonaphasics during language tasks. Finally, functional MRI, which images the activation area in the brain by detecting the reduced concentration of deoxy-Hb during neuronal activation, should be performed on the patients with cerebral dysfunction, giving special consideration to the possible multiplicity of the rCBF and cerebral oxygen metabolism responses to functional tasks.